The present invention relates to a measurement device for a head gimbal assembly. More specifically, the present invention relates to a method of and an apparatus for measuring torque and stiffness in the range of one micro-Newton meter and below for a head-gimbal assembly.
FIG. 1 illustrates a hard disk drive design typical in the art. Magnetic recording hard disk drives 100 use a read/write transducer or head mounted on an air-bearing slider for reading and/or writing data to a disk. The slider is attached to an actuator arm by a suspension. The combination of the slider and suspension is called a head-gimbal assembly (HGA) 102. The HGA uses the suspension for manipulating the read/write transducers throughout the disk. Typically, suspensions are miniature sheet metal springs that are very flexible. The sheet metal springs are in part rotational springs with stiffness values below one micro-Newton-meter per degree. Measuring these springs has become a challenge when trying to evaluate this parameter exactly as it operates in the disk drive. In addition, measuring torque in the range of one micro-Newton meter and below is difficult. For accurate measurement of this range of torques, the minimum resolution needed is below 0.05 micro-Newton meters. However, the most sensitive torque transducers in the market today cannot measure below 35 micro-Newton meters.
Several problems also exist with the methods used today to measure torque and stiffness of HGA suspensions. Most of the methods used today, including those known as “static” or “dynamic,” introduce extra parts such as relatively large bars that must be bonded to sliders. Adding these extra parts tends to introduce inaccuracies in the results due to the geometric variations in manufacturing these extra parts. Another problem with existing methods is that the parts being tested do not experience the exact boundary conditions as they do in their final state in the disk drive. One missing boundary condition is Z-height. Both “static” and “dynamic” measurement methods mount the HGAs on the testers in a state different from their natural state in the disk drive. Similarly, “static” and “dynamic” methods do not exert the correct load onto the air bearing of the slider. As a result, both of these methods produce results that are often questionable as to their accuracy and/or validity.
Thus, what is needed is an improved method and apparatus for measuring the stiffness and torque of a HGA in the range of one micro-Newton meter and below.